1. Field of the Invention
This invention relates to a strut type suspension of a vehicle and, more particularly, to a suspension used for a front wheel suspension and connected with a steering gear.
2. Description of the Prior Art
A strut type suspension is so structured that a strut has an upper strut portion and a lower strut portion capable of sliding relative to the upper strut portion, the upper strut portion is swingably connected to a vehicle body and the lower strut portion is swingably connected to a suspension arm extending in a lateral direction of the vehicle body.
Since the above suspension has features that the number of points mounted on the vehicle body is small and a lateral member is limited only to the suspension arm, it has the advantages that an input to the vehicle body is small, an accuracy in working hardly affects suspension geometry, and a lateral special restrictions are few. On the contrary, the suspension involves a problem that a change in camber of a tire is small in bounding, so that a camber to the ground of a turning outer wheel is enlarged at the positive side.
There are various proposals in order to enlarge the change in chamber of the tire in bounding. For instance, there are a proposal disclosed in Japanese Patent Public Disclosure (KOKAI) No. 56-82613 as shown in FIG. 21 and that disclosed in Japanese Patent Public Disclosure (KOKAI No. 63-28707 as shown in FIG. 22.
In a suspension as shown in FIG. 21, an upper strut portion 21 of a strut 20 is swingably connected to a vehicle body 23, and a lower strut portion 22 capable of sliding relative to the upper strut portion 21 is swingably connected to a suspension arm 24 extending in a lateral direction of the vehicle body. A portion of a wheel carrier 25 located above a rotary axis of a wheel is swingably connected to an assist link 27 through a ball joint 26. This assist link 27 is swingably connected to the lower strut portion 22, and a portion of the wheel carrier 25 located below the rotary axis is swingably connected to the suspension arm 24 through a ball joint 28.
In a suspension as shown in FIG. 22, the upper strut portion 21 of the strut 20 is swingably connected to the vehicle body 23, and the lower strut portion 22 is swingably connected to an upwardly extending portion of an L-shaped suspension arm 30 extending in the lateral direction of the vehicle body and upwardly. A portion of a wheel carrier 31, the wheel carrier 31 being formed into a substantially reversed C-shape as viewed from the back, located above a rotary axis is swingably connected to the lower strut portion 22, and a portion of the wheel carrier 31 located below the rotary axis is swingably connected to the corner of the suspension arm 30.
Now, in order to cope with the development of high-performance of a front wheel drive car, which is a so-called FF car, for example, the development of high performance through mounting a high output engine, it is necessary for each front wheel to restrain as much as possible from tending to rotate around a steering axis, that is, a kingpin axis at a time of rapid acceleration or deceleration to thereby ensure controllability.
The front wheel tends to rotate rearward around the kingpin axis by means of a braking force acting on the center of a grounding contact surface of the tire, and also tends to rotate forward around the kingpin axis by means of a driving force acting on a point intersecting the rotary axis of the tire and an imaginary vertical plane passing through the center of the grounding contact surface of the tire each other. The degree of rotation produced by the braking force varies according to the amount of a kingpin offset which is defined by a distance between the intersection of the kingpin axis and the ground surface and the center of the grounding contact surface of the tire. Also, the degree of rotation produced by the driving force varies according to the amount of a distance between the intersection of the imaginary vertical plane passing through the center of the grounding contact surface of the tire and the rotary axis of the tire and the kingpin axis, the distance being a so-called IK distance. In order to restrain the front wheel from tending to rotate around the kingpin axis as far as possible, the kingpin offset and the IK distance should be brought to zero or as close as possible to zero.
The kingpin axis in the case of FIG. 21 is provided as a line connecting the center of the ball joint 26 with the center of the ball joint 28. As is apparent from the drawing, the ball joints 26, 28 may be disposed so as to locate outward in the lateral direction of the vehicle body in order to bring the kingpin offset L.sub.1 to zero and also bring the IK distance L.sub.2 as close as possible to zero.
On the other hand, the link 27 should be shortened in order to enlarge the change in a camber angle having a negative tendency. In order to shorten the link 27 and bring the kingpin offset and the IK distance to zero or as close as possible to zero, the lower ball joint 28 should be naturally disposed outward in the lateral direction of the vehicle body.
However, in condition that the ball joint 28 is located outward in the lateral direction of the vehicle body, when the swing angle of the ball joint 28 relative to the wheel carrier 25 is large during the swing of the suspension arm 24, interference of the ball joint 28 with the wheel or a brake device provided on the wheel carrier occurs, so that such interference should be avoided. As a result, it is limited to dispose the ball joint 28 outward of the vehicle body.
The suspension shown in FIG. 22 involves the similar problems.